The present invention relates generally to catheter assemblies, and more particularly to a catheter having a fluid control valve in the distal end thereof for controlling delivery of fluids from the catheter to the blood flow passage in which it is inserted, and vice versa.
Various procedures for intravenous therapy, including hyperalimentation and the administration of chemotherapeutic drugs, require the use of a catheter which remains in the patient's body for a period of days, weeks, or even months. In a typical procedure, the catheter is inserted through the subclavian vein, located near the collar bone and advanced to the superior vena cava, an area of substantial blood flow to the heart. In some long term catheterization procedures, the physician reroutes the exposed end of the catheter from the original entry, near the collar bone, subcutaneously through the patient's body and out into the abdominal area so that the patient can resume normal activities without having a catheter protruding from the collar bone area.
Such catheterization procedures have been performed routinely with a conventional catheter having an open distal end. By the term "distal" is meant the leading edge of the catheter upon insertion into the body. Blood flow out of the body is prevented by occluding a portion of the catheter which is external to the patient's body, such as by covering the portion of the catheter outside the body by an injection cap which includes a pierceable septum for allowing injection and withdrawal of fluids.
This form of catheter has certain disadvantages in that the open end of the catheter, which is positioned in the patient's body, provides an area for the formation of blood clots. The potential for formation of clots is undesirable because clots occlude the catheter and prevent its use. Furthermore, a clot can separate from the catheter and travel to other areas of the vascular system and cause injury by occluding another blood vessel. The open distal end type of catheter must be flushed frequently with a heparinized saline solution to clean the catheter area and reduce the potential for clot formation.
This periodic maintenance provides a potential for irritation and infection by manipulation of the catheter and introduces an anticoagulant into the blood stream which may affect the patient or any blood test results from specimens taken from the patient. In addition, the external cap may be removed inadvertently which creates the danger of introducing an air embolus into a vein and injuring the patient. Furthermore, the blunt open end of the catheter interferes with blood flow and is believed to increase the occurrence of turbulent eddies which eddies may also promote clot formation.
Such problems are avoided if the central venous catheter is provided with a closed distal end with a port or valve arrangement. U.S. Pat. No. 3,111,125 teaches a shunt apparatus with an outlet tube having a closed distal end and a plurality of slits around the periphery of the distal end of the tube acting as slit valves. Fluid pressure in the tube forces the slits open so that fluid flows freely when a sufficient pressure differential exists between the fluid within the tube, and the area outside the tube. Along these lines, U.S. Pat. Nos. 4,559,046 and 4,701,166 teach a catheter device for intravenous therapy having a flexible closed distal end including a slit-type valve as described above with, in addition, a twisted wire removable stiffener which is used to facilitate insertion of the catheter into a patient and then removed, leaving the catheter in place.
A valve is desirable in a central venous catheter for controlling fluid flow through the catheter and into the patient, as described above and further to allow fluid flow from the patient's vascular system out of the catheter when obtaining, for example, a blood sample. Slit valves of past structures present problems because inwardly directed pressure tends to shut the slit valve more tightly rather than to open it. U.S. Pat. Nos. 4,559,046 and 4,701,166, as discussed above, teach the use of soft materials such as silicone rubber to overcome this problem which silicone rubber is made in a thin cross-section and treated with dimethylsiloxane for lubrication of the slit edges and for weakening, and making the catheter wall more pliable, in order to facilitate the two-way valve function.
However, this form of slit-type valve works well only where outward flow is desirable and inward flow is not desirable because of its directional properties. Because the distal end of the catheter is made of softer material and further treated to be weaker in order to attempt to overcome deficiencies of a pressure activated slit valve, the tip of the catheter becomes weaker.
This weakened tip is more prone to bending caused by patient movement or muscular movement within the patient's body and the tip may be bent in such a manner as to open the valve in the absence of fluid pressure differential across the valve. A weakened tip will also be more prone to collapse during aspiration. Also, silicone lubrication can wear off making it difficult to open the valve during aspiration. There is a trade-off, therefore, between optimizing the valve performance so that the valve is responsive to fluid pressure differentials, and providing a valve that stays shut when required and is strong enough not to collapse during aspiration.
There is still a need for a reliable, easily fabricated catheter having a closed distal end and a valve which will minimize the potential for damage to cellular elements in liquid passing through the valve, which can be used successfully for aspiration without collapsing, while at the same time minimizing the potential for inadvertent opening of the valve. Such inadvertent opening can result in patient blood loss or the introduction of an air embolus into the patient's vascular system or formation of a clot in the lumen.
One such arrangement is taught in co-pending application Ser. No. 881,148, filed Jul. 2, 1986 now U.S. Pat. No. 4,737,152, issued Apr. 12, 1988 wherein the fluid control valve has a cylindrical side wall describing a lumen therethrough, a proximal end and a closed distal end, and includes a slit through the side wall positioned adjacent the distal end with the slit angularly oriented with respect to the longitudinal axis of the catheter.
The slit is defined by two opposed faces formed in the side wall. The catheter housing includes a conduit wherein the proximal end of the catheter is connected to the housing so that the conduit and lumen are in fluid communication. A stylet is positioned within the lumen. A valve control knob includes a passageway therethrough, and is rotatably connected to the housing so that the passageway and the conduit are in fluid communication. The knob engages the stylet causing rotation of the stylet, which in turn causes rotation of the closed distal end of the catheter causing the opposed faces of the slit to separate, forming an opening for allowing fluid communication between the lumen and the exterior of the catheter.
This arrangement has the advantage that the operator is allowed to selectively open and shut the valve regardless of pressure differentials. However, this arrangement is more complicated in that it includes considerably more structure in order to open and close the valve.
With this invention, by contrast, a valve arrangement is provided in the form of a slit valve which responds to pressure differentials on either side of the valve, without causing the catheter to collapse. Moreover, the arrangement is such that the forward end of the catheter includes a closed distal end which is comprised of sufficient body that it will not bend or become occluded because of body movements of the patient, muscular movements of the patient or aspiration vacuum. Moreover, the valve in the form of a slit, in accordance with this invention, is provided in a comparatively thin wall covering the distal opening of the catheter, so that it responds rapidly to pressure differentials on either side thereof. Because of this, the valve opens readily to the presence of medication being fed into the catheter for introduction into the blood supply of the patient. By the same token, the valve opens in response to the opposite pressure differential for obtaining a blood sample from the patient, as required.
This is achieved by selecting a conventional catheter with an open distal end and providing a sheath covering over that open distal end. In this way, the structural integrity of the catheter wall is not altered. The sheath has the effect of forming a dual wall structure over the end of the catheter adjacent the distal end thereof while providing a single thin wall in the area of the slit valve. Because of this, the thin wall in which the valve of the invention is positioned responds much more rapidly than would be the case if the valve were positioned in the conventional thicker wall of the catheter body itself. Nevertheless, with the dual wall structure in the areas other than where the valve is positioned, the catheter distal end has more "body" for sustaining less damage and/or injury from patient movement, readjustment of the positioning of the valve of the invention or aspiration vacuum. More importantly, there is less involvement in the structural integrity of the catheter wall than is the case when a slit is positioned in the catheter wall itself.
In considering generally the conditions for forming the catheter valve assembly of the invention, preferably the catheter is comprised of polyurethane having a thickness within the range of 10 and 30 mils. Positioned-over the open distal end of the catheter is a sheath comprised, preferably, of the same material as the catheter i.e., polyurethane. The sheath wall is of a thickness within the range of 2 and 10 mils. It should be understood that the sheath may be comprised of a material different from the catheter wall itself. Other materials for forming either or both of the catheter and the sheath may include, for example, silicone rubber, polyvinylchloride, polyethylene or polytetrafluoroethylene.
As discussed above, the slit forming the valve of the invention is positioned in the sheath in the area where the sheath does not cover a portion of the wall of the catheter itself, such as the immediate distal end thereof. As a result, the thickness of the wall surrounding the slit valve of the invention will be within the range of 2 and 10 mils which causes the slit valve to respond much more rapidly to pressure differentials on either side thereof. Nevertheless, the adjacent wall of the catheter itself surrounding the valve wall will have a thickness within the range of 12 and 40 mils, thus providing more body for the catheter adjacent to the valve.
As a result, because the distal end of the catheter is not open, blood reflux in the catheter lumen is eliminated thereby eliminating the potential for clot formation, and occlusion of the catheter. As a result of this, routine flushing of the catheter lumen is not necessary. Moreover, because there is a valve covering the open end of the catheter, introduction of air embolus into the vasculature is eliminated, should the injection cap on the proximal end of the catheter outside the body be removed or fall off.
Of course, turbulent eddies are reduced around the open end of the lumen of the catheter since it is not open and is protected by the thin wall of the sheath of the invention carrying the slit valve. Because of this, potential clot formation on the exterior wall of the catheter is reduced. Finally, because the material adjacent the valve is not treated to weaken it (because it is not necessary) there is much less chance of failure.
As further illustrative of the invention herein, the sheath may be within the range of between about 5 and 20 millimeters in length. The slit valve may be of a length within the range of between about 30 and 70 percent of the inner diameter of the catheter.
Other objects and advantages of this invention will be apparent from the following description, the accompanying drawings, and the appended claims.